Method of making agglomerates



Patented May 27, 1952 METHOD OF MAKING AGGLOMERATES Thomas'W. Bartram,St. Albans, W. Va., assignor to Monsanto Chemical Compan St. Louis, Mo.,a corporation of Delaware No Drawing.

' 10 Claims.

This invention relates to improved dust free compositions and methods ofmaking same. More particularly it relates to a method of making readilydispersible dust free compositions for rubber compounding.

Copending application of Monte, Throdahl, Serial No. 106,328 filed July22, 1949, and now abandoned, describes the preparation of dustlessbead-like agglomerates from rubber accelerators. The general method ofpreparation involves heating a slurry of the accelerator to beagglomerated in the presence of 33-55 parts by weight of a suitablebinding agent per 100 parts by weight of accelerator with subsequentcooling and separation of the bead-like particles. Continuation-impartapplication of Monte C. Throdahl, Serial No. 188,899 and application ofKenneth E. Creed, Jr., Serial No. 183,897 of even date herewith disclosethat agglomeration may be efiected by continued heating and stirring,the cooling step becoming incidental. means particles containing -55parts binder per 100 of accelerator could be produced and other rubbercompounding agents agglomerated. The

binding agents employed are waxy materials as.

for example, parafiin but preferably a waxy material having a polargroup like stearic acid. This invention relates to improvements in thisprocess employing a waxy material having a polar group as one of theconstituents.

The process proved to be somewhat erratic with certain accelerators andantioxidants. For ex-- ample, the time necessary to produce agglomeratesvaried considerably or conditions of the process such as rate ofstirring, temperature and other variables had to be controlled preciselyfor reproducible results.

In accordance with this invention it has been discovered that morereproducible results are obtained if in addition to a polar bindingagent there is added to the slurry a small amount of an essentiallyneutral water insoluble organic material. Best results have beenobtained with colloids like glue. In the presence of glue the bead-likeagglomerates are more stable as well as less erratic in formation.Occasionally a run which apparently starts to aggregate satisfactorilydisintegrates on continued stirring and heating whereas in the presenceof glue the agglomerating reaction continues normally. It is believedthat glue has a seeding effect inproviding a nucleus on which particlescan grow although the invention is not limited to any theory of the modein which the agents function to produce the results observed. The effectappears to be physical since a wide variety of ma- Application SeptemberSerial No. 183,898

2 terials of diverse chemical nature are satisfactory. The essentialcharacteristics are that the material be water insoluble but capable ofproducing a uniform fine dispersion.

Tetramethyl thiuram disulfide is a typical example of a rubberaccelerator advantageously agglomerated in the. presence of glue. Thisaccelerator may be used directly in the form of a slurry obtained by theoxidation of sodium dimethyl dithiocarbamate, the usual .method ofmanufacture. The invention will be illustrated employing the method ofCooper, U. $2,375,083, wherein oxidation is effected by chlorine but itis by no means limited thereto. Seventy parts by weight of 'tetramethylthiuram disulfide contained in an aqueous slurry of approximately 20%concentration obtained by the oxidation of sodium dimethyldithiocarbamate with chlorine was charged into a suitable container. Onepart of hide glue was dissolved in the dispersion or preferably added asa 2% solution and the pH adjusted to 3.5-4.5 by means of dilutehydrochloric acid. Thirty parts by weight of stearic acid were added andthe mixture heated at a temperature in the range of 65 C. whilesubjecting to eflicient agitation until bead-like agglomerates of thedesired size were produced.v

The reaction was then terminated by quickly cooling with an excess ofcold water, the particles filtered oil, washed and dried. Usually theparticles are larger than 40 mesh by the time the temperature reachesabout 62? C.

Dispersions of substantially 70 parts by weight of tetramethyl thiuramdisulfide in 280 parts by weight of water were prepared and the pHadjusted to 5-6. Substantially 25 parts by weight stearic acid was addedand substantially 5 parts by weight of one of the additives listed belowand the mixture stirred and heated at about 65 C. until particulatebead-like agglomerates larger than 40 mesh were produced. The resultsare tabulated below:

In another series of preparations illustrative of the invention the basechange was similar to that described above namely,

parts by. weight of.

soluble essentially neutral organic binder in uniform finely divideddispersion, and heating at 60-70 C. while continuing the stirring untilbead-like agglomerates larger than 40 mesh are formed.

'7. The process of making a dustless freefiowing accelerator compositionfurther characterized by very rapid dispersion into a rubber on millingwhich comprises subjecting to agitation an acidic aqueous dispersion oftetramethyl thiuram disulfide in the presence of approxi-- mately 33-55parts by weight per 100 of the tetramethyl thiuram disulfide of stearicacid and in addition thereto 1-10 parts by weight per 100 of thetetramethyl thiuram disulfide of glue and heating at 60-65 C. whilecontinuing the stirring until bead-like agglomerates larger than 40 meshare formed.

8. The process of making a dustless freeflowing accelerator compositionfurther characterized by very rapid dispersion into a rubber whichcomprises subjecting to agitation an acidic aqueous dispersion of about70 parts by weight of tetramethyl thiuram disulfide and about 30 partsby weight of binder consisting in stearic acid and glue, the glue beingabout l-10 parts by weight per 100 of the tetramethyl thiuram disulfideand heating at 60-65 C. until bead-like agglomerates larger than 40 meshare formed.

9. The process of making a dustless freefiowing accelerator compositionfurther characterized by very rapid dispersion into a rubber on millingwhich comprises subjecting to agitation an acidic aqueous dispersion of1,3-bis(2-benzothiazolylmercaptomethyl) urea in the presence ofapproximately 3355 parts by weight per 100 of the1,3-bis(2-benzothiazolylmercaptomethyl) urea of a higher fatty acid andin addition thereto 110 parts by weight per 100 of the l,3-bis(2-benzothiazolylmercaptomethyl)urea of an essentially neutral organiccolloid and heating while continuing the stirring until bead-likeagglomerates larger than 40 mesh are formed.

10. The process of making a dustless freefiowing accelerator compositionfurther characterized by very rapid dispersion into a rubber on millingwhich comprises subjecting to agitation an acidic aqueous dispersion ofabout '70 parts by weight of 1,3-bis(2-benzothiazolylmercaptomethyl)urea in the presence of approximately parts by weight stearic acid andin addition thereto 1-10 parts by weight per 100 of the1,3-bis(2-benzothiazolylmercaptomethyl)urea of glue and heating whilecontinuing the stirring until bead-like agglomerates larger than 40 meshare formed.

THOMAS W. BARTRAM.

REFERENCES CITED Thev following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,326,984 Tomlin Aug. 1'7, 19432,343,835 Smith Mar. 7, 1944

1. THE PROCESS OF MAKING AN IMPROVED DUSTLESS COMPOSITION FOR RUBBERCOMPOUNDING WHICH COMPRISES SUBJECTING TO AGITATION AN ACIDIC AQUEOUSDISPERSION OF A MIXTURE OF AN ORGANIC WATER INSOLUBLE ACCELERATORMELTING ABOVE 100* C., A WAXY BINDER CONTAINING A POLAR GROUP IN ABOUT5-55 PARTS BY WEIGHT PER 100 PARTS OF ACCELERATOR, AND A WATER INSOLUBLEESSENTIALLY NEUTRAL ORGANIC BINDER IN ABOUT 1-10 PARTS BY WEIGHT PER 100PARTS OF ACCELERATOR AND HEATING WHILE CONTINUING THE STIRRING UNTILBEAD-LIKE AGGLOMERATES LARGER THAN 40 MESH ARE FORMED.